Hi bkay - looked at a few videos of the Westalee system and I can see how maybe? raising the throat plate (which is how the 401/403 and 500/503 "drop" their feed dogs) may not be preferable. I would consider just taking the feed dogs off. The Chapman midget ratchet and some of the bits are ideal to get under there and take the feed dogs out when the throat plate is off...they make a sewing machine repair kit too. Also I'd be sure to use the straight stitch throat plate "AK3" too (unless you had occasion to zig zag with that system)
That said I've had a pretty good time darning with the throat plate raised to the darn position, and wonder if this wouldn't work for you also.
Matt